In clamping devices of this type, the clamping jaw is stressed for bending in its center part which is weakened by the provision of the opening for the locking screw. In order to lend said clamping jaw the necessary bending stiffness, it must be constructed particularly high or thick in the center part or, however, also very wide. At any rate, such a bulky construction of the clamping jaw forms an obstacle for the discharging chips which are formed during the machining process. This is primarily annoying during an internal working, where the chip has only a limited area for its discharge. Random and irregularly formed chips are created in the openings through the clamping jaw, which occupy the entire free space and often cause considerable breakdowns, such as blade breakage and the forcing away of the drill rod by wedged-in chip balls, diameter deviations and roughed-up or rather damaged surfaces. If one forms such clamping jaws with small dimensions in the center part, then they do not have the necessary clamping force generating capabilities.
The basic purpose of the invention is to provide a clamping device of the above-mentioned type in which the clamping jaw projects as little as possible above the chip surface and thus assures a good chip discharge, wherein the clamping jaw, however, also assures a good clamping with a high amount of clamping power. In a further embodiment of the invention, the clamping device is also inexpensive to manufacture and has improved handling capabilities.
The basic purpose of the invention is attained by the clamping jaw having in its center part on its side facing the turnable cutter blade a substantially cylindrical projection which is arranged coaxially with respect to the opening, and in which is continued the opening for the locking screw, and that in the tool holder there is provided a cylindrical recess which is arranged coaxially with respect to an internally threaded opening therein, and in which recess is received the projection of the clamping jaw.
Through this embodiment it is achieved that the clamping jaw has a high resistance to bending and simultaneously projects little beyond the chip surface of the turnable cutter blade. The projection which is provided on the underside of the clamping jaw namely increases the bending stiffness of the center part very substantially. Since, however, the projection on the underside of the clamping jaw projects into the tool holder, it does not at all interfere with the chip discharge. The clamping jaw can be kept extremely flat.
Furthermore, it is preferable if the opening in the center part of the clamping jaw on the upper side of the same has an enlarged section for the complete reception of the screwhead. In this manner, it is assured also that no chips can get caught on the screwhead.
The bottom wall of this enlarged segment preferably has a ball-cup-shaped construction and the pressure surface of the screwhead, which surface faces the bottomwall, has a segment of a sphere shape. In this manner, it is possible with possible height variations between the upper side of the turnable cutter blade and the support surface for the rear lever arm on the tool holder to adjust the clamping jaw to the respective conditions and still have the screwhead rest with its entire periphery on the clamping jaw.
The projection is preferably tapered slightly toward its free end and has a frustum of a cone shape, wherein the angle of the cone is approximately 10.degree. or less. Through this frustum-shaped construction, the clamping jaw is centered with respect to the cylindrical receiving opening, even when said opening is not completely occupied. Thus, it is assured that the clamping jaw rests always on the predetermined point of the upper side of the turnable cutter blade.
The clamping jaw has furthermore preferably two equally long lever arms and is constructed as a rotationally symmetrical swivel part, which has two lateral flattened edge portions which extend parallel with respect to the longitudinal axis of the lever arms and parallel to one another, and which extend approximately tangentially with respect to the surface of the projection. Through this embodiment, the clamping jaw can be manufactured inexpensively as a swivel part. The lateral flattened edge portions can be manufactured by milling in a simple manner.